Ground pressure
Ground pressure is the pressure exerted on the ground by the tires or tracks of a motorized vehicle, and is one measure of its potential mobility, especially over soft ground. Ground pressure is measured in pascals (Pa) which corresponds to the EES unit of pounds per square inch (psi). Average ground pressure can be calculated using the standard formula for average pressure: P'' = ''F/''A''. In an idealized case, i.e. a static, uniform net force normal to level ground at Earth sea level, this is simply the object's weight divided by contact area. The ground pressure of motorized vehicles is often compared to the ground pressure of a human foot, which can be 60 - 80 kPa while walking or as much as 13 MPa for a person in spike heels. Increasing the size of the contact area on the ground (the footprint) in relation to the weight decreases the ground pressure. Ground pressure of 14 Pa (2 psi) or less is recommended for fragile ecosystems like marshes. Decreasing the ground pressure increases the flotation, allowing easier passage of the body over soft terrain. This is often observed in activities like snowshoeing. Example Ground Pressures All examples are approximate, and will vary based on conditions Hovercraft: 0.7 kPa (0.1 psi) Human on Snowshoes: 3.5 kPa (0.5 psi) Rubber-tracked ATV: 5.165 kPa (0.75 psi) Diedrich D-50 - T2 Drilling rig: 26.2 kPa (3.8 psi) Human male (1.8 meter tall, medium build): 55 kPa (8 psi) M1 Abrams tank: 103 kPa (15 psi) 1993 Toyota 4Runner / Hilux Surf: 170 kPa (25 psi) Adult horse (550 kg, 1250 lb): 170 kPa (25 psi) Passenger car: 205 kPa (30 psi) Wheeled ATV: 240 kPa (35 psi) Mountain bicycle: 245 kPa (40 psi) Racing bicycle: 620 kPa (90 psi) Note: Pressures for Man and Horse are for standing still. A walking human will exert more than double his standing pressure. A galloping horse will exert up to 3.5 MPa (500 psi). The ground pressure for a pneumatic tire is roughly equal to its inflation pressure. Low ground pressure vehicles Often called LGP Vehicle. These are vehicles which are designed to reduce the contact pressure to avoid sinking in on soft ground or to avoid damage to fragile surfaces. The best known examples of the main methods used are machines with Caterpillar tracks or fitted with flotation tyres. Notable LGP vehicles on bogtracks]] * Bogtracks(swamp) - Supper wide version used on machinery to work on peat bogs, swamps or in marshy conditions. The most extreme examples can work in water by floating. * Terra Gator - tractors fitted with Terra tyres, used for spreading fertilizer and spraying and in the Netherlands fitter with dumper bodies to haul materials on land reclamation schemes. used on the tidal mudflats in Cumbria]] * Bandvagen 206(Hagglunds) snow cat - used by the military and by rescue servies for snow, soft sand and marsh work. * Floating excavators excavators fitted with pontoon floats with tracks for extremely soft or wet conditions often used to clean canals and water course or to dredge ponds of weed and silt. See also *Contact patch *Tire load sensitivity * Glossary Index Related reading * Theory of Ground Vehicles References Category:Automotive engineering Category:Physical quantities Category:Low ground pressure